Albert Barnes Commentary Hebrews 7:15

"And [what we say] is yet more abundantly evident, if after the likeness of Melchizedek there ariseth another priest," — Hebrews 7:15 (ASV)

And it is yet far more evident. This greater evidence does not pertain to our Lord springing out of Judah. Instead, the point he was endeavoring to establish—that there must be a change of the priesthood—was made still more evident by another consideration.

A strong proof of the necessity of such a change of the priesthood was supplied by the fact that the Messiah was to be of the tribe of Judah. However, an even stronger proof arose because, as a priest, He was to be of the order of Melchizedek—meaning He was of the same rank as one who did not even belong to that tribe.

After the similitude (meaning "resembling"); that is, He was to be of the order of Melchizedek.